This invention relates to a waveshape memory to be employed for an electronic musical instrument and other tone generation devices and, more particularly, to a waveshape memory storing waveshape data in a compressed form of representation and thereby enabling reduction in the required memory capacity.
In a prior art waveshape memory for an electronic musical instrument, waveshape data is stored directly in linear or logarithmic representation format. This requires a large bit number resulting in increase in the memory capacity. If, particularly, waveshape data for one sample point is of a large bit number in a case where a tone waveshape signal of a high quality equivalent to a tone of a natural musical instrument is to be obtained by storing a full waveshape or a waveshape of plural periods from the start to the end of generation of a tone in a memory and reading the waveshape from this memory, the memory capacity as a whole becomes extremely large. An attempt to reduce the bit number of data for one sample point tends to reduce the dynamic range thereby impairing the tone quality of the tone produced.
An electronic musical instrument of a type in which, in the above described manner, a full waveshape from the start to the end of generation of a tone is prestored for each key (note) in linear representation format and this waveshape is read out is disclosed in the specification of U.S. Pat. No. 4,383,462. In the waveshape memory WM31 shown in FIG. 3 of this U.S. patent, the full waveshape is stored in linear representation format and this full waveshape is read out in response to a signal KD which represents a key depression timing.
While there is no prior art of a memory in which a full waveshape is stored in a logarithmic representation format, storing of a full waveshape in a logarithmic representation format will be naturally conceived, for there is a well known art of storing a waveshape of one period in a logarithmic representation format and thereby simplifying an operation circuit in utilizing an output read-out signal for multiplication and division.